Raw hydrocarbon fuel is catalytically reformed into a hydrogen rich fuel gas prior to being fed into the power section of a fuel cell power plant. The reforming of the raw fuel is typically performed in catalytic beds disposed in tubular containers which are enclosed in a reformer housing. The raw fuel mixed with steam will be fed into the reformer housing and into the catalyst beds, and the reformed fuel gas is drawn off of the catalyst beds and removed from the housing for transfer to the power section. The reformer housing will also include a burner which heats the tubes and catalyst beds to operative temperatures for supporting the reaction. In the larger fuel cell power plants which have higher power ratings, each reformer housing will contain a number of catalyst tubes, all of which should be heated to the same extent for optimum reformer efficiency. These larger reformer housings will typically have a single burner to heat all of the catalyst tubes, so that a problem arises as to how all of the tubes in the housing will be heated to the same optimum temperature with only one burner. This problem of evenly distributing the heat from the reformer burner among all of the catalyst tubes is addressed in U.S. Pat. No. 4,661,323 to O. L. Olesen, granted Apr. 28, 1987. The aforesaid patent discloses the use of ceramic sleeves which are fitted onto the catalyst bed tubes. The sleeves are provided with a plurality of helical grooves which are cut into the bores of the sleeves and which provide flow paths for the hot burner gases around the outside of the tubes. The helical grooves are separated from each other by helical lands which engage the tubes in curvilinear planar contact. The helical lands overlie and cover about 25 to 35% of the external surface of the catalyst tubes, and thus actually insulate the catalyst tubes from the heated gases to a significant degree. This is, of course undesirable, and limits the efficiency of the reformer so that the fuel being reformed must be passed through the reformer at a slower rate to ensure the proper degree of reformation of the raw fuel to the hydrogen rich fuel gas. Another problem arising with the prior art ceramic sleeves relates to their inelasticity, which renders it difficult to properly fit them onto the metal catalyst tubes. Finally, the different coefficients of thermal expansion and contraction between the metal tubes and ceramic sleeves creates problems with the interfit while the reformer is in operation. In operation, there will be a temperature difference of from 300.degree. to 500.degree. F. from the top of the catalyst tubes to the bottom, with a reformer of the type shown in U.S. Pat. No. 4,661,323, referred to above.